Friday, November 1, 2013

So it took me a couple of days, but I finally got around to adding support for joysticks in INDI. This is very exciting and it became quite important recently when I started using EQMod driver. For now, all LX200 and EQMod drivers supported. I didn't put a lot of
functionality into the telescope drivers joystick control section yet,
just the basic N/S/E/W motion and selection of slew speeds.

This is particular useful for EQMOd where it was a pain to try to center
any star using the INDI control panel, while at the same time, trying
to look in the eye piece! Of course, now with Ekos Alignment module
& astrometry.net solver I don't have to do that anymore, but this
functionality is indeed essentials for all of those tired of jumping
back and forth between the scope and the laptop.

All those features will be available in the next INDI Library v0.9.7 release.

Sunday, October 27, 2013

Yesterday, I field tested Ekos Alignment Module using EQMod for Linux driver with my Orion Atlas telescope. The module utilizes astrometry.net solver to find the actual celestial coordinates in a given image, making scope alignment quite a trivial procedure with amazingly accurate GOTOs.

To use Ekos for alignment, first you have to put your telescope in the starting home position, which simply means that it should be leveled and pointed at the North Celestial Pole (NCP), if you are in the northern hemisphere. With my mount (HEQ5), I have a polar finder scope so pointing it at the NCP was quite trivial simply by adjusting the mount altitude and azimuth knobs until polaris is within a small circle designated in the polar find scope.

Next, I fired Ekos and started it with two drivers: EQMod & QSI CCD INDI drivers. It would have been possible to use the Synscan driver, but the driver is very limited compared to EQMod. After you use EQMod, you never look back.

Then I asked EQMod to track a nearby star. Now this is where the magic of Ekos comes. You don't have to do anything yourself! No more looking in the eye piece or CCD image to align your scope. You just hit "solve" and it figures where in the sky the telescope is really pointing. Once it finds a solution, you can ask it to either sync the telescope coordinates to the solution coordinates, or sync and slew back to the target we were tracking just earlier. I set it to "Slew to Target" and I had to stop the first iteration of the solver because it was taking too long, but after adjusting some options (as you can see in the video), the solver only took 8 seconds to find a solution.

Each time the solver finds a solution and syncs, an alignment point is added to EQMod Alignment Model, which is N-Star by default. The more alignment points you have, the more accurate your slews become. I then asked EQMod to track another nearby star and repeated the same process, this time the solver only took 2 seconds. Finally, to show that the alignment is really working, I slewed to M31, took an image, and it was dead in the center!

All those exciting Ekos features are coming up in the next KDE 4.12 release. Have to give a shout-out to Jean-Luc Levaire, INDI EQMod driver developer, and Dustin Lang from astrometry.net for all their hard and beautiful work!

Saturday, October 12, 2013

Any amateur astronomer must have experienced the woes of aligning their mount. First, your mount has to be aligned with the polar axis. Second, you need to perform an alignment procedure to enable the built-in GOTO firmware to slew and track your objects of choice. Often we are offered to align the mount with 2 or 3 bright stars spread all over the sky which then enables the firmware to build a simple model for the mount errors that it has to correct for when it slews to a target. Also, at this point, the firmware knows where the telescope is looking at in the sky, or so it thinks as we find out below.

While the simple 2 or 3 star alignment is often sufficient for visual observation, it becomes a source of frustration in astrophotography. After slewing to your target, you often have to perform framing to center the actual object within the CCD desired field of view. Once that's done, your mount is now tracking the object, and you can begin to take your photos.

For deep sky astrophotography, you typically have to take multiple long exposures frames and later stack them. The mount tracks the object sidereally (i.e. in RA), but most commercial mounts suffer from manufacturing defects in the worm gears and other parts that makes accurate sidereal tracking difficult. Furthermore, your mount has to be perfectly aligned with the earth polar axis as any deviation will cause tracking errors.

This is where Ekos Alignment module comes into play. Alignment module performs the following:

Highly accurate GOTO.

Determine polar alignment errors.

Ekos Alignment Module

The way it works is by capturing an image of a star field, feeding that image to astrometry.net solver, and getting the central coordinates (RA, DEC) of the image. The solver essentially performs a pattern recognition against a catalog of millions of stars. Once the coordinates are determined, the true pointing of the telescope is known. Often, there is a discrepancy between where the telescope thinks it is looking at and where it is truly pointing. The magnitude of this discrepancy can range from a few arcminutes to a couple of degrees. Ekos can then correct the discrepancy by either syncing to the new coordinates, or by slewing the mount to the desired target originally requested.

Furthermore, Ekos can measure the misalignment in the polar axix by taking a couple of images near the meridian and east/west of the meridian. This will enable the user to adjust the mount until the misalignment is minimized.

With the addition of the alignment module, Ekos is now the ultimate astrophotographer tool under Linux!

Saturday, April 20, 2013

Last week, I attempted to capture an image for the beautiful galaxy pair M81 & M82 in the constellation of Ursa Major. Since I live in a heavily light polluted city in Kuwait, I knew that broadband imaging is quite challenging, and was quite shocked when I found out that the background level due to light pollution noise cuts half the dynamic range of the CCD!

So even after processing, I ended up with a quite poor image:

So I decided to pick my gear, and head to AlSalmy, which is an isolated desert area northwest of Kuwait. While the skies there are not as dark as I'd like it to be, it's the best thing we have in Kuwait, for the time being at least as I'm pretty sure light pollution will ruin it within a decade or less. The trip was well worth the effort, and despite a waxing gibbous moon that lured close to the zenith, the background noise was substantially better than the inner city, no surprises here.

Here is the final image, taken with Ekos, and processed with PixInsight.

Friday, March 29, 2013

For the last couple of years, I have been working on building a 5 meter radio telescope for educational purposes in my free time. Its primary purpose is to map neutral hydrogen distribution in the milky way. Hydrogen, the simplest atom, shines at the radio frequency of 1.42 Ghz (or 21 cm line), and we use multistage amplifiers to boost the very weak radio signal to something that can be processed by the electronics of a spectrometer.

Using INDI + KStars as the control platform, the user can command the telescope to slew and track objects. Slewing to an object is quite trivial. The telescope is equipped with absolute optical multiturn encoders that provide the positional feedback to the control system. If we know the home position of the telescope and the encoder to degrees ratio, it would be possible to command the dish to move to a new position and stop whenever the new desired angle is reached. Tracking, however, is another matter.

The telescope motion is in Alt-Az (Altitude-Azimuth) while objects rotate due to the motion of the earth from east to west at sidereal rate. Hence, both altitude and azimuth axis must move in a step-wise ladder direction to keep up with the sidereal motion. Due to limitation in the mechanical system of the dish, the minimum speed of both axis is still a lot faster than the sidereal rate, and therefore, tracking was developed to keep the object within the beamwidth of the radio dish, which is 3 degrees, at all times via a user configurable tracking threshold. Whenever the threshold is exceeded, the dish corrects itself using the minimum speed possible.

The following is a screenshot taken for the creatively named J065514.3+540858 radio source in the constellation of Lynx. It is a relatively bright radio source with integrated flux of 1371 mJy @ 1.42 Ghz.

In the next few days, the goal is to fine tune the pointing accuracy and to calibrate the overall system noise. Finally, I'd like to thanks the developers of Kst for making such a great program! I use Kst to stream real time measurements from the continuum spectrometer, and this saved a lot of development time and effort. Kudos to the Kst team!